Heterotopic ossification (HO) that complicates acetabular fractures is initiated at the time of injury.19 We hypothesised that indomethacin medication commenced prior to surgery and within the first week following injury would be more effective than post-operative use alone. Over a four-year period 184 consecutive patients with significantly displaced acetabular fractures scheduled for acetabular reconstructive surgery were included in the study. Fifty-seven patients received indomethacin post-operatively only (Group 1), 95 pre- and post-operatively (Group 2), and 19 received no treatment for various reasons including intolerance of NSAIDs(Group 3). Three patients died and ten were lost to follow-up. Standard AP radiographs were reviewed at 2 weeks, 6 weeks, 3 months, 6 months and 12 months post-op and were grading as per Brooker on the 3-month follow-up radiograph. The mean Brooker values for Group 1 = 0.70; Group 2 = 0.33; Group 3 = 1.57. A statistical analysis of the p-values for Group 1 compared to Group 2 = 0.04; Group 1 to Group 3 = 0.002; Group 2 to Group 3 = 0.000006. Associated injury was the only parameter that correlated with increasing heterotopic ossification, while age, sex, approach and fracture type had no influence. This study confirms that indomethacin reduces the incidence and severity of HO in acetabular fracture surgery and is more effective if started pre-operatively.